I rode in a truck yesterday with an odd problem. 12valve auto. Well tuned pump, large injectors. Running a 62/71/.8 over GT42-02. At 5 psi in the manifold, the primary gauge is just lifting off the peg( same as my similar sized setup). From there it gets weird. At 50psi in the manifold, he's about 40psi in the cold pipe. At one point we saw 50 psi off the primary and about 75psi overall. The truck is no slouch, but 50psi from a 75mm charger is a bunch of air. Another kicker is that it shows the same numbers with a full sized(75/96/1.32 S400) primary. It is just a bit slower to rise. Changing top charger makes no difference either. He has run all the way up to a 66/71/.8. Changing wastegate opening pressures does not affect the numbers. Even setting it all the way up to 60psi. Seat of the pants says that the power is not matching the boost numbers. Multiple primaries, multiple secondaries, same problem. Drive pressure is just slightly more than boost at the manifold. Watching the primary gauge is weird. It goes up really fast with just a bit of throttle.?????

Ron

 

That makes me think one of the gauges is suspect.

Were different gauges tried?

 

Yes, different gauges have been tried.

Ron

 

You don't by chance have a temp probe in between stages to see what the charge air temp is?

Any idea on the pre cac boosted air temp?

 

Is the wastegate working on that primary Ron? Or are you trying to push it?

Dave

 

You are thinking the the primary seems to spool too fast? Bragging about the GT42-02 or actually a problem?

Sounds to me more like a problem with the secondary. I have no experience per say so I guess I am just throwing some garbage out there.

Jim